The invention relates to a measuring module for the measurement and testing of an object, having a measuring chamber that can be evacuated that is to hold the object to be measured and having a contact element, wherein the object to be measured is thermally connected to a first contact surface of the contact element during the measurement and/or test operation, and having at least one cold head that can be thermally connected to a second contact surface of the contact element, wherein the cold head can be cooled down to cryogenic temperatures using a cryo-refrigerator comprising at least one cold stage, and wherein the contact element consists of material with high thermal conductivity, and the first and second contact surfaces are located on opposite sides of the contact element, wherein the cold head and the contact element are thermally conductively interconnected during the measurement and/or testing operation in an environment that can be evacuated.
Such a measurement device is known from [2].
The thermal noise of electronic components can be reduced by cooling. The thermal noise arises due to statistical movements of the charge carriers and due to irregular, temperature-dependent grid oscillations that are transferred to the charge carriers by pulses. It manifests itself as a noise voltage VR at the ends of electrical conductors. At an ohmic resistance R that is at temperature T, the noise voltage in the frequency range Δf is calculated as [3], [4]:|VR|=√{square root over (4kRT−Δf)} where k=1.38·10−23 Ws/K (=Boltzmann constant)
Reducing the temperature T of metal conductors also reduces their resistance R so that the product R·T and therefore the thermal noise voltage VR is especially greatly reduced. For this reason, this cooling method is used today for sensitive measuring instruments and sensors, such as are found, for example, in NMR spectroscopy [1]. A clear improvement in measurement sensitivity is achieved in such cases, i.e. the signal-to-noise ratio (=SINO).
For the development of such measuring instruments or sensors with cooled electrical or electronic components, suitable electronic or electrical components (e.g. cables, resistors, transistors, etc.) must be assessed in advance and undergo quality control testing (e.g. thermal cycling). For this purpose, test systems are required that enable the cooling of individual electronic components and whole electronic circuits down to their operating and test temperature with the aim of determining their properties and specifications and to conduct quality control tests on them.
The simplest and most widespread method of cooling to cryogenic temperatures is to use liquid nitrogen (LN2) or in rarer cases, liquid helium (LHe). The components to be measured (electronic components or circuits, mechanical components, or combinations thereof) are immersed in a Dewar vessel filled with LN2 or LHe. Quality control tests (e.g. thermal cycling tests) and/or determination of electrical and mechanical properties of components can be performed in this way.
The disadvantages of this method are that the lowest cryogenic temperature is dependent on the boiling temperature of the liquid gas 77K for LN2 and 4.2K for LHe), and the test samples are exposed to extreme thermal stress due to the high cooling rates. Moreover, water condensation and ice can form on the samples.
In a somewhat more advanced cooling method, the object to be cooled measured is attached to a contact element with high thermal conductivity that is cooled down to the desired temperature by a refrigerant (e.g. LN2 or LHe). To keep thermal losses low, the entire configuration is housed in an evacuated chamber, which avoids the formation of condensation and ice [2]. However, such systems are only efficient at temperatures just above the boiling point of the refrigerant. If test samples have to be tested far above the boiling point (but still far below room temperature), this must be performed by additional heating of the contact element, which in turn results in increased loss of refrigerant and increased costs (especially if the refrigerant is LHe). A further disadvantage in this case is that the user is always reliant on the refrigerant and must ensure that a sufficient stock of it is available. Such a set-up also has the disadvantage that the user must be versed in the handling of cryogenic liquids.
In addition to this, measuring modules are known in which the cooling is not performed by a cryogenic refrigerant but a cryo-refrigerator with a closed refrigerating circuit [2]. The disadvantage of this measuring module is that the cryo-refrigerator first has to be switched off, followed by a long waiting time before the cryo-refrigerator has warmed up sufficiently for the chamber in which the test sample is located to be opened.
Based on this prior art, the object of the invention is to propose a measuring module and a measuring device with which such long waiting times can be avoided to make cooling the objects to be measured more convenient.